1. Field of the Invention
The present invention relates to a motor-driving system using a pulse width modulation signal having an optimized pulse waveform.
2. Description of the Related Art
In recent years, with the aim of realizing safer, more secure, and more comfortable cars, cars powered by a motor generator, such as hybrid cars or electric cars, have increased in number.
In such a car, torque is generated by driving a motor generator using power from a battery to obtain the driving force of the car. At this time, a power converter is used to convert DC power from the battery to AC power. The power converter receives DC power from the battery and converts this DC power to three-phase AC power. Here, it is desirable to reduce power loss in the power converter and the motor generator as much as possible, to thereby allow more effective utilization of the power from the battery.
In response to this situation, there are disclosed techniques for reducing power loss due to heat generation by switching a switching element included in a power converter. For example, there is disclosed a method for eliminating, in a three-phase full-bridge power converter, components which are equal to or greater than the fifth order harmonic components of a rectangular wave from a particular phase thereof. Further, there is also disclosed a technique in which, if switching is performed M times during a half-cycle, a waveform is set to have half-wave symmetry and odd symmetry, thereby reducing harmonic components.
A low-order harmonic cancellation PWM which only considers reducing low-order harmonic components of power input by switching a power converter was disclosed, and does not consider current distortion and effects on torque that are caused when driving voltage is applied to a motor generator. Therefore, for example, iron loss of the motor generator which is caused by harmonic components of current is also not taken into consideration, and thus control is not carried out in consideration of loss of the entire driving system including a power converter and a motor generator.